Vehicle brake



Feb. 26, 1946.

J. S. IRVING ET AL VEHICLE BRAKE Filed Aug. 24, 1944 M wzivyi,

WW m Patented Feb. 26, 1946 UNITED STATES PATENT OFFICE v John Samueland Thomas Mace, Bllmihgham, Ell gland Applibaififin August '24, 1944,Serial 550,922 In Great Britain thine 1-2, 1943 1 Claims.

This invention relates to --in-iprovments "in vehicle brakes and refersparticularly to brakes of the type in which a pair of opposed shoesmounted within a brake drum are adaptedto be urged outwardly intocontact with the drum by separating or spreading means arranged betweenthe shoes at one end, and the shoes are permitted a limitedcircumferential movement with respect to the drum when the brake isapplied.

One object of our invention is to provide simple and "efiective sh'oeseparating "means for a brake of this type which permits substantialvariation of the effort applied to the individual shoes according torequirements and enables a powerful braking effort to be obtained with arelatively small applying force.

According to our invention the adjacent ends of a. pair of opposed shoesare adapted to be separated by angular movement of a floating leverengaging at spaced points with staggered abutments on the shoe ends andthe lever has a rolling fulcrum on a surface on the back-plate of thebrake or on a part mounted thereon which surface is inclined withrespect to the plane of the back-plate so that movement of the fulcrumalong the surface varies theeifective spacing of the fulcrum from theplane of the back-plate. This variation can be used to vary the relativeeifort applied to the shoes in proportion dependent on the spacingbetween the points of the engagement of the lever with the shoes and theful crum and the inclination of the surface on which the fulcrum rolls.

One practical arrangement is shown by way of example in the accompanyingdrawing in which:

Figure 1 is a plan of the shoe separating mechanism and the adjacentshoe ends.

Figure 2 is an elevation.

Figure- 3 is an elevation of the steady post in which the mechanism ishoused.

In Figures 1 and 2, 10, 11 are the brake shoes and 12, 13 are the shoewebs. The webs are extended beyond the end of the shoes and the extendedparts are offset on opposite sides of the central plane of the shoes asshown in Figure l. The lengths of the extended parts of the webs aresuch that they overlap slightly in the off position of the brake, andtheir extremities are received in notches in opposite sides of a,cylindrical steady post M which is secured to the backplate l of thebrake and forms a stop for the shoes in the off position of the brake.

The shoe webs are located against lateral disback-plate and to itsfree-"end is pivotally 'c'onneoted a fork 'e'n'd Ill "extending through"an openplacement by cranking a tongue portion of each out of alignmentwith the rest to bear on each side of the post as s hown'at 16in Figures1 and 2.

stantially at right angles to the back-plate between the ends of theshoe webs, the inner edge of the arm engaging the web I2 which isfurthest from the back-plate and the outer edge of the arm engaging theother web I3. The long arm of the lever extends substantially parallel.to the ing 20 in the back-plate. The fork end is adapted to receive apull-rod 2! or other means for applying a force to the lever in adirection substantially at right angles to the back-plate.

On the long limb of the lever adjacent the junction of the limbs thereis a lug 22 notched to receive the reduced central part of a roller 23of bobbin form. This roller engages a track 24 which is formed by theinner end'of the slot I1 and is inclined at an angle to the back-plate.

When a pull is applied to the free end of the long limb of the lever ina direction at right angles to the back-plate the lever rocks about theroller 22 as a fulcrum and the short arm of the lever applies oppositelydirected thrusts to the end of the shoe webs to urge the shoes outwardlyinto engagement with the drum I5a. The roller meanwhile rolls down theinclined track 24 until one shoe engages the drum and the lever thencontinues to roll down the inclined track while fulcruming on theextremity of the Web of the stationary shoe until both shoes are in fullengagement with the drum.

The reaction on the roller is at right angles to the inclined track andthis results in different braking efforts being applied to the twoshoes.

Whether this efiect is an increase or decrease of the braking effortapplied to one particular shoe depends on the direction of inclinationof the track 24 relative to the direction of rotation of the drum, butnormally the arrangement will be such that application of the brakecauses a greater load to be applied to the trailing shoe than to theleading shoe. The difference in the loading of the two shoes isdependent solely on the inclination of the track 23 relative to theplane of the back-plate.

In the embodiment illustrated the lever engages with staggered abutmentsformed by offsetting extensions of the shoe webs but the abutplane ofthe shoes.

We claim:

1. A vehicle brake comprising a rotatable drum, a stationary back-plate,shoes mounted within the drum for limited circumferential movementtherewith when the shoes are brought into contact with the drum,staggered abutments on adjacent shoe ends, a floating lever engagingbetween said abutments, a surface on the backplate with which the leverhas a rolling fulcrum engagement and inclined with respect to the planeof the back-plate, and means for rocking the lever about its fulcrum toseparate the shoe ends.

2. A vehicle brake comprising a rotatable drum, a stationary back-plate,shoes mounted within the drum for limited circumferential movementtherewith when the shoes are brought into contact with the drum,staggered abutment-s on adjacent shoe ends, an L shaped floating leverhaving one arm extending substantially at right angles to the back-platebetween said abutments and a, long arm'extending substantially parallelto the back-plate, a roller mounted on the long arm of the leveradjacent the junction of the arms, a surface on the back-plate withwhich said roller engages to form a rolling fulcrum for the lever ofwhich the surface is inclined with respect to the plane of thebackplate, and means for applying a force to the long arm of the leverin a direction substantially at right angles to the back-plate to movethe lever angularly about the roller as a fulcrum.

3. A vehicle brake comprising a rotatable drum, a stationary back-plate,shoes mounted within the drum for limited circumferential movementtherewith when the shoes are brought into contact with the drum,staggered abutments on adjacent shoe ends, a steady post mounted on theback-plate and extending between the said abutments, staggered notchesinthe post on opposite sides thereof into which said abutments enter, alongitudinal slot in the post intersected by said notches, an inclinedend surface to said slot adjacent the back-plate, a floating leverhoused in said slot between said abutments and having a rolling fulcrumengagement with said inclined surface, and means for applying a turningmovement to the lever.

4. A vehicle brake comprising a rotatable drum, a stationary back-plate,shoes mounted within the drum for relative separation into engagementtherewith, staggered abutments On adjacent shoe ends, a, floating leverengaging be. tween the abutments and a surface on the backplate withwhich said lever has a rolling fulcrum engagement and which is inclinedwith respect to the plane of the back-plate.

- JOHN SAMUEL IRVING.

T. K. MACE.

